This invention relates to a fluid pump dispenser of a type having a pump body with a pump cylinder defining a pump chamber, and a valve-controlled product inlet passage leading to the chamber. A manually reciprocable pump plunger has a hollow stem defining a valve controlled discharge passage leading from the chamber to a discharge spout on an outer end of the stem, and a pump piston mounted on an inner end of the stem for relative sliding movement, the body having a plunger return spring for biasing the plunger into a raised position.
Fluid pump dispensers generally of the aforementioned type are known, although many of the known dispensers have certain disadvantages in that while offering a high level of technical improvements are often costly to produce and assemble while others, if economical, have significantly reduced technical advantages.
U.S. Pat. No. 5,615,806 discloses a plunger lock-up dispenser which operates by manually depressing a plunger/spout for lowering a hollow plunger stem to which a pump piston is attached thereby pressurizing primed liquid in the pump chamber defined by a pump cylinder of the dispenser body. A piston return spring located within the pump chamber extends between the piston and a throat portion of the pump body and forms a ball cage or an inlet ball check valve at the throat portion. The piston is mounted for limited sliding movement on the stem such that during the pressure stroke the piston uncovers discharge ports in the stem permitting fluid under pressure to be discharged through the discharge passage and spout. A quantity of product is dispensed from the chamber upon a full stroke of the piston, the quantity being in proportion to the length of the piston stroke. On the upstroke the piston returns to its raised position under the influence of the spring thereby expanding the chamber and reducing the chamber pressure causing product to be suctioned into the chamber through the open inlet valve from the liquid container to which the pump dispenser is mounted.
As in all manually operated dispensers the chamber must be primed with product to displace air in the chamber. Air is initially evacuated by stroking the plunger. However with such a prior art structural arrangement the compressible air in the chamber oftentimes causes the stem and piston to travel in unison without uncovering to the discharge ports for evacuating the chamber air until the end of the downstroke at which the stem travels slightly downwardly at the bottom end of the piston stroke for uncovering the discharge ports. On the return stroke the ports are closed and product is drawn into the expanding chamber via the unseated inlet ball check valve.
Such dispensers are principally designed to dispense liquid soaps and the like, a fluid of average viscosity, although on many occasions attempts to proportion low viscosity fluids fail, due to the fact that the nature of the seals in the seal-tight areas is relatively imperfect. Moreover, satisfactory results are difficult to achieve for dispensing high viscosity fluids, or variable (gel type) viscosity fluids, given that widespread use of such fluids is relatively recent and the inner passages of the pump dispenser are not adapted to them.